1. Field of the Invention
The present invention relates to an ink jet recording apparatus including a recording head and an ink tank.
2. Description of the Related Art
Conventional ink jet recording apparatuses include so-called serial-scanning-type apparatuses in which a recording head, serving as recording means, and an ink tank, serving as an ink container, are exchangeably mounted on a carriage movable in a main scanning direction. In this recording method, an image is sequentially recorded on a recording medium by repeating main scanning by the carriage on which the recording head and the ink tank are mounted, and sub-scanning on the recording medium.
This recording method can record an image on a large-size recording medium, such as an A1 or A0 size sheet, by providing the carriage with a large moving width. However, since an image is recorded using a large amount of ink on a large sheet, the amount of ink accommodation of the ink tank must be increased, resulting in an increase in the weight and inertia of the entire carriage, and, as a result, an increase in the force needed to move the carriage. In order to move the carriage at a high speed, it is necessary to provide a high-output carriage driving motor having large driving power, resulting in an increase in the cost of the entire recording apparatus. In accordance with an increase in the weight of the entire carriage, a force for decelerating the carriage to a stopped position such as when the carriage changes direction in reciprocating main scanning also increases, and the entire recording apparatus vibrates in reaction to that force. Accordingly, it is difficult to realize a high moving speed of the carriage.
On the other hand, when reducing the amount of ink accommodation of the ink tank in order to reduce the weight of the carriage, the frequency of exchange of the ink tank increases. In some cases, the ink tank must be exchanged in the midst of a recording operation.
A technique described in Japanese Patent Application Laid-Open (Kokai) No. 9-24698 (1997) has been proposed as a solution for solving the above-described problems relating to exchange of the ink tank. In this known technique, a closed bag-type ink container is connected to a recording head. By connecting an auxiliary ink container to the bag-type ink container whenever necessary, ink is replenished from the auxiliary ink container to the bag-type ink container. The bag-type ink container includes a bag for accommodating ink, and accommodates ink within the bag under a negative pressure having a value sufficient to prevent leakage of ink from ink discharging ports of the recording head. Ink is replenished from the auxiliary ink container to the bag-type ink container using the negative pressure in the bag.
The bag in the bag-type ink container is pressed in accordance with the amount of ink discharge of the recording head, i.e., in accordance with the amount of use of ink, to reduce its volume. When the volume of the bag decreases to a value equal to or less than a predetermined amount, a tap of a supply port provided at the bag-type ink container is opened to connect the supply port to the auxiliary ink container. As a result, ink is replenished from the auxiliary ink container into the bag due to the negative pressure within the bag. When the amount of ink accommodated within the bag has a maximum value, the negative pressure within the bag becomes xe2x80x9c0xe2x80x9d, so that replenishment of ink is automatically stopped. According to this known technique, replenishment of ink can be automatically stopped using the negative pressure without requiring control using a pressure sensor, a volume detection sensor, or the like.
The upper limit of the negative pressure in the bag-type ink container is determined in consideration of an ink discharging force when the recording head discharges ink, because when the negative pressure is too large, the ink discharging force of the recording head decreases due to the negative pressure, resulting in faulty ink discharge. Accordingly, it is necessary to determine the negative pressure within a range of good ink discharging conditions in the recording head. It is also necessary to set the head position of ink in the auxiliary ink container to a position lower than the head position of ink in the bag-type ink container. If the difference between the head positions of the two containers is too large, it is impossible to replenish ink even if the negative pressure in the bag-type ink container is determined in accordance with the ink discharging conditions of the recording head.
Accordingly, in this known technique, a special device is provided in order to set the position of the auxiliary ink container in the vertical direction with respect to the bag-type ink container. However, provision of such a device causes the problem that the size and the cost of the entire recording apparatus increase. Furthermore, if air enters an ink channel connecting the auxiliary ink container and the bag-type ink container during replenishment of ink, the air moves into the bag of the bag-type ink container, to greatly reduce the amount of ink accommodation of the bag-type ink container. In addition, if the amount of penetration of air is large, the bag within the biased-bag-type ink container is filled with the air, resulting in incapability of ink replenishment. Another problem is that, since the bag-type ink container is configured by an elastic bag material for forming the bag, and movable members, such as a spring member for inflating the bag, and the like, there is a limitation in reduction of the size, thereby causing complexity in the structure, an increase in the weight, and an increase in the production cost.
It is an object of the present invention to address the above-described problems in the known technique, while reducing the size and the weight of an ink jet recording apparatus and improving its reliability.
According to one aspect, the present invention which achieves these objectives relates to an ink-jet recording apparatus including an ink tank for receiving ink from an ink intake, ink supply means for receiving ink from a replenishing tank into the ink tank by a negative pressure introduced from a suction port of the ink tank in the inside of the ink tank, and negative-pressure control means for causing the negative pressure within the ink tank to remain in an ink supply channel from the replenishing tank to the inside of the ink tank, so that the negative pressure within the ink tank does not return to an atmospheric pressure while receiving ink.
In one embodiment, the negative-pressure control means includes sealing means, provided within the ink tank, for sealing the ink supply channel with a predetermined negative pressure value.
In another embodiment, the sealing means includes a spring or an elastic member.
According to another aspect, the present invention which achieves these objectives relates to an ink-jet recording apparatus including an ink tank for receiving ink from an ink intake, ink supply means for receiving ink via an ink supply channel from a replenishing tank to the inside of the ink tank by a negative pressure introduced from a suction port of the ink tank in the inside of the ink tank, connection means, provided between the ink intake of the ink tank and the ink supply channel, capable of being separated from the ink intake, and negative-pressure control means for causing the negative pressure within the ink tank to remain in the ink supply channel, so that the negative pressure within the ink tank does not return to an atmospheric pressure while receiving ink.
In one embodiment, the negative-pressure control means includes sealing means, provided within the ink tank, for sealing the ink supply channel with a predetermined negative pressure value.
In another embodiment, the negative-pressure control means includes sealing means, provided at the connection means, for sealing the ink supply channel with a predetermined negative pressure value.
In still another embodiment, the sealing means includes a spring or an elastic member.
In yet another embodiment, the apparatus also includes gas-liquid separation means, provided at the suction port, for allowing a gas permeate without allowing passing ink to permeate.
In yet a further embodiment, the gas-liquid separation means is one of a tetrafluoroethylene resin and a similar porous resin material which allows a gas to permeate without allowing a liquid to permeate.
According to still another aspect, the present invention which achieves these objectives relates to an ink supply system including a stationary ink tank for storing ink to be supplied to a recording head, including an ink reservoir, which performs scanning parallel to a recording medium whenever necessary, and an ink supply channel for connecting the ink tank to the ink reservoir, and suction means for producing negative pressure in the inside of the ink reservoir of the recording head. The ink supply channel is connected to the ink reservoir of the recording head during ink supply, and ink is supplied from the ink tank to the ink reservoir of the recording head via the ink supply channel by suctioning the inside of the ink reservoir by the suction means. The system also includes an opening/closing mechanism for closing a communicating state between the ink supply channel and the ink reservoir before a negative pressure state within the ink reservoir returns to an atmospheric pressure by replenishment of ink.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.